Pig system

ABSTRACT

In a system for loading a liquid into a tank truck by means of a pipeline, a pig is used for pushing product through the line toward the truck. This pig is stored at the source end of the line and is caused to move through the line first toward the truck end, and then back to its storage location at the source end, all in response to the operation of a &#39;&#39;&#39;&#39;pig start&#39;&#39;&#39;&#39; pushbutton.

United States Patent McNealet al.

[151 3,665,954 [451 May 30,1972

[ PIG SYSTEM [72] Inventors: Donald A. McNeal, Brookhaven, Pa.; Paul A.Dearry, Wilmington, Del.

Sun Oil Company, Philadelphia, Pa.

Feb. 17, 1971 [73] Assignee:

[22] Filed:

[21] Appl.No.: 116,079

52 U.S.Cl ..137/268, l5/l04.06 s1 58 Field of Search ..137/268;l5/l04.06 A, 104.06 B

[56] References Cited 7 UNITED STATES PATENTS 3,021,703 2/1962 Pfrehm..73/3 3,273,375 9/1966 Howe ..73/3

3,421,360 1/1969 Luse et al. ..73/3 3,455,143 7/1969 Shamp ..73/3 3,580,045 5/ 1971 Pfrehm ..73/ 3 Primary Examiner-M. Cary Nelson AssistantExaminer--Robert J. Miller Anomey-George L. Church, Donald R. Johnson,Wilmer E. McCor-quodale, Jr. and Frank A. Rechif [57] ABSTRACT 12Claims, SDrawing Figures 00/0704 FAA/E L 520p TIM/Ir Patented May 30,1972 3,665,954

3 Sheets-Sheet 2 FIG. 2

97 y 22 l l/ PULSE 5 SHAPING CIRCUIT Q6 I! I f 1W ATTY.

Patented May 30, 1972 3,665,954

3 Sheets-Shoot 5 FIG. 212

DUAL

PULSE SHAPING CIRCUIT mvcmons: DONALD A. McNEAL PAUL A. D ARRY "1 65 1,v ATTV PIG SYSTEM This invention relates to a pig system, and moreparticularly to a system of this type for loading a liquid into a tanktruck by means of a pipeline.

in the distribution of petroleum products, it is a fairly commonpractice to mix or formulate any grade of product desired, as the needarises, in a source tank, the quantity of product so formulated beingexactly that required to fill one tank truck. The source tank may besome distance away from the truck loading rack, such as 500 feet. Sinceonly the exact quantity of product necessary for filling a truck hasbeen formulated in the source tank, some means must be provided formoving the final increment of liquid through the pipeline to the truck,after the tank has been pumped dry; in this connection, it is pointedout that the volume of liquid contained in 500 feet of 4-inch diameterpipe is approximately 325 gallons. In addition to this topping off" ofthe truck, it is of course desirable to clean the line after eachdelivery, in order to prevent contamination of one product by adifferent product which was previously present in the line.

According to this invention, a pig is stored in what amounts to acontinuation of the pipeline, at the source tank end thereof. When it isdesired to top off" the tank truck to complete a delivery, the main pumpis stopped and, in response to operation thereafter of a pig start"pushbutton, compressed air is applied to one side of the pig to drive itthrough the line to the loading rack or tank truck end, the pig thenpushing the liquid ahead of it toward the truck. When the pig reachesthe loading rack end of the line, compressed air is automaticallyapplied to the other side of the pig to drive it through the line in theopposite direction, thereby to return it to its starting point (at thesource tank end of the line).

A detailed description of the invention follows, taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a diagrammatic illustration of a tank truck loading systemutilizing this invention;

FIGS. 2a and 2b, taken together, comprise a schematic of the controlcircuit utilized in the invention; and

FIGS. 3 and 4 are elevational views of a pig utilized in the invention.

First referring to FIG. I, which is a diagrammatic illustration of atank truck loading system, the items at the left-hand side of thisfigure are all located at the blending or source tank end of the system,while the items at the right-hand side are all located at the oppositeor loading rack end of the system.

The source tank 1 is used to mix or formulate any grade of product whichis desired to be shipped by tank truck; this tank may be located about500 feet away from the truck loading rack. Once an order is received andprocessed, the ordered product is formulated in the source tank 1 in theexact amount called for by the order.

A loading pump 2, which is remotely operated from a control panel 3located near the loading rack, draws its intake or suction from tank 1through a manually operated gate valve 4. The operation of this pumpwill be described further hereinafter. The discharge of pump 2 is fedthrough a pump discharge valve 5 (solenoid-operated) to thesmaller-diameter arm of a reducing tee fitting or coupling 6, and thencethrough a pipeline 7 (for example, 4 inches in diameter, about 500 feetin length, and also coupled to the tee) to the loading rack, at which atank truck 8 is positioned for loading. A guard bar, 1% X A X about 3inches long, is welded across the smaller-diameter arm of tee 6, flushwith the inside diameter of the run of the tee.

At the loading rack end of line 7, a reducing tee fitting or coupling 9(similar to tee 6, and including a similar guard bar) is coupled to line7, and from the smaller-diameter arm of this tee a fluid conduit extendsthrough a loading rack valve 10 (solenoid-operated) and a manuallyoperated shutoff valve 11 to a spout or nozzle 12 suitable fordispensing the fluid into the tank truck 8. A parallel or bypass conduit(connected essentially in parallel with items 11 and 12, and usefulmainly in extraordinary or emergency situations) extends from a pointbetween valves 10 and 11, through a manually operated valve 13 and asmaller-diameter line 14 to a slop tank 15. Thus, if the tank truck 8becomes full while the pump 2 is still running, valve 11 can be closedand valve 13 opened to divert the excess product to the slop tank 15.

At the blending or source tank end of line 7, a rather short piece 16 of4-inch diameter pipe (some 4 to 6 feet in length, for example) extendsbetween the tee 6 and a flange 17. A pig, to be further describedhereinafter, is normally stored" in the length of pipe 16. A system foroperating this pig, which system will be later described, is remotelyoperated from the control panel 3. Two other lines, each three-fourthsinch in diameter for example, are coupled to the flange 17. One is avent-drain line 18 leading to a slop sump, and has therein a source tankvent valve 19 (solenoid-operated); the other is an air supply line 20(connected to a compressed air supply of 60 psig), which has therein asource tank air supply valve 21 (also solenoid-operated) and a checkvalve (schematically indicated) to keep oil from the air supply. Apig-operated switch 22, which is operated by the passage of a pigthereby, is associated with pipe 16. This switch will be furtherreferred to hereinafter.

At the loading rack end of line 7, a short piece 23 of 4-inch pipe(similar to pipe 16) extends between the tee 9 and a flange 24. Twoother lines, one three-fourths inch in diameter for example, and one 1%inches in diameter for example, are coupled to the flange 24. The 1%inches one is a vent-drain line 25 leading to a slop sump, and hastherein a rack vent valve 26 (solenoid-operated); the three-fourth-inchone is a compressed air supply line 27, which has therein a loading rackair supply valve 28 (also solenoid-operated) and a check valve(schematically illustrated) to keep the air supply free of oil. Apig-operated switch 29, operated by the passage of a pig thereby, isassociated with line 7, a short distance from tee 9 in the direction ofthe source tank, and a similar pig-operated switch 30 is associated withpipe 23. Switches 29 and 30 will be further referred to hereinafter.

A detailed description of the operation of the invention will behereinafter given, in connection with the circuit diagram of FIGS.2a-2b. However, a brief, general description now follows. Assuming thatthe truck 8 is positioned for loading, the loading pump 2 is started toempty the source tank 1 into the truck 8 by way of line 7, valves 4, 5,l0, and 11 all being open and valves 13, 19, 21, 26, and 28closed. Whentank 1 is empty, pump 2 is stopped, and a pig is caused to move throughline 7, from its "home in pipe 16 toward the rack end of line 7. In sodoing, it pushes the liquid product ahead of it to top off" the truck 8.Any excess is pushed to the slop tank 15, by closing valve 11 andopening valve 13. When the pig reaches the loading rack end of the line,it is returned automatically to its home" in pipe 16.

Refer now to the circuit diagram of FIGS. 2a-2b. The components in FIG.2a are located in a relay box adjacent the source tank end of thesystem, while those in FIG. 2b are located at a control shelter, nearthe loading rack end of the system. A multiconductor cable 31interconnects the components located at the two ends of the system.

When the system is not in use, the vent 19 at the source tank end andthe vent 26 at the rack end are both open. These vents are bothsolenoid-operated, being of the latch-open, trip-close type; the opencoil 19" for vent 19 and the open coil 26" for vent 26 have both beenenergized near the end of the previous operation, as will be describedhereinafter, so that these vents are at this time latched open. Allother solenoid valves are closed, these latter being of theenergize-to-open type, and being unenergized when the system is not inuse. At this time, the pig (whose construction will hereinafter bedescribed) is in its rest or home or stored position, in pipe 16,between tee 6 and flange 17; this is at the source tank end of the line7.

Assuming that the order has been formulated in source tank 1 and thatthe tank truck 8 is positioned for loading, a start" pushbutton 32,located in the control panel 3 (at the control shelter, near the loadingrack) is depressed to start the operation. This pushbutton isillustrated as operating a double-pole, single-throw momentary contactswitch. The normally closed relay contacts 33 being closed, anenergization circuit is completed for vent trip relay 34 when pushbutton32 is operated, this circuit extending from the positive bus 35 throughthe upper pair of contacts 36 of pushbutton switch 32, through thewinding of relay 34 to the negative bus 37; likewise, an energizationcircuit is completed for vent trip relay 38 through contacts 36 andthrough the winding of this latter relay to bus 37. The closing ofcontacts 39 of relay 34 completes an a.c. energization circuit for trip"winding 19' of vent valve 19, causing this valve to trip closed; theclosing of contacts 40 of relay 38 completes an a.c. energizationcircuit for "trip" winding 26' of vent valve 26, causing this lattervalve to trip closed.

When "start" pushbutton 32 is operated, an energization circuit iscompleted for relay 41, from bus 35 through the lower pair of contacts42 of switch 32, through the winding of relay 41 to bus 37. The normallyclosed relay contacts 43 being closed, closure of contacts 44 of relay41 completes an a.c. energization circuit for winding 46 of a motorcontactor relay 45, closing the contacts 47 of this latter relay andenergizing the motor 2' for pump 2 from the a.c. line. This starts pump2. Contactor relay 45, when energized, locks itself in through a pair oflocking contacts 48 and the closed contacts 43.

When relay 41 is energized, closure of its contacts 49 completes anenergization circuit through the winding 50 of a relay 51, causing thecontacts 52 of this latter relay to close. Closure of contacts 52energizes the solenoid of ball valve (pump discharge valve) 5, openingthis latter valve. Relay 51, when energized, locks itself in through apair of locking contacts 53 and a pair of normally closed relay contacts54.

Operation of start" pushbutton 32 completes an energization circuit forrelay 55, from bus 35 through contacts 42 of switch 32, through thewinding of relay 55 to bus 37. Closure of the contacts 56 of relay 55completes an obvious energization circuit through winding 57 of relay58. Closure of contacts 59 of relay 58 energizes the solenoid of ballvalve (loading rack valve) 10, opening this latter valve. Relay 58, whenenergized, locks itself in through a pair of locking contacts 60 and apair of normally closed relay contacts 61.

When pushbutton 32 is operated, an energization circuit is completed fora pig hold relay 62, through the switch contacts 36 and through thewinding of relay 62; energization of relay 62 opens its normally closedcontacts 63 and thus prevents any circuit being completed by operationof a pig start pushbutton 64 whose contacts are connected in series withcontacts 63. Pig hold relay 62, when energized, locks itself in througha pair of locking contacts 65 and a pair of normally closed contacts 66of a pig release relay 67.

When the motor contactor relay 45 is energized, closure of its contacts68 completes an a.c. energization circuit through closed contacts 43 tothe winding 69 of a relay 70; closure of the contacts 71 of relay 70completes an a.c. energization circuit through the pump indicating light72 on the control panel 3 and this light goes on, indicating that thepump 2 is on.

The vents 19 and 26 and air source valves 21 and 28 at both ends of theline 7 being closed, and valves 5 and 10 both being open, pump 2 pumpsproduct from the source tank 1 through line 7 and into tank truck 8.

When pumping of the product from source tank 1 has been completed, astop pushbutton 73, located in the control panel 3, is depressed. Thispushbutton, like pushbutton 32, is illustrated as operating adouble-pole, single-throw momentary contact switch. The normally closedrelay contacts 33 still being closed, an energization circuit iscompleted for relay 74, from the positive bus 35 through the upper pairof contacts 75 of pushbutton switch 73, through the winding of relay 74to the negative bus 37. Energization of relay 74 causes opening of itsnonnally closed contacts 43 and 54, previously mentioned. Opening of thecontacts 43 releases motor contactor relay 45, opening its contacts 47and deenergizing pump motor 2. Pump 2 thus shuts down.

Opening of the contacts 54 releases relay 51, opening its contacts 52and deenergizing the ball valve solenoid 5, causing the pump dischargevalve 5 to close.

Opening of contacts 43 breaks the energization circuit for relay 70;opening of the contacts 71 then breaks the circuit through light 72, andthis light goes out.

Upon operation of pushbutton 73, an energization circuit is completedfor the pig release relay 67, from the positive bus 35 through the lowerpair of contacts 76 of pushbutton switch 73, through the winding ofrelay 67 to the negative bus 37. Energization of relay 67 causes openingof its normally closed contacts 66, previously mentioned. Opening ofcontacts 66 releases the pig hold relay 62, allowing its contacts 63 toreclose.

After the pump is stopped, the pig system is put into operation, forautomatic topping off" of the truck. This is done by depressing the pigstart" pushbutton 64, located in the control panel 3. Pushbutton 64 isillustrated as operating a double-pole, single-throw momentary contactswitch. Relay contacts 63 being closed, an energization circuit is thencompleted for a relay 77, from the positive bus 35 through the upperpair of contacts 78 of pushbutton switch 64, through the winding ofrelay 77 to the negative bus 37. Relay 77, when energized, locks itselfin through a pair of locking contacts 79 and the normally closedcontacts 80 of a relay 81.

Closure of contacts 82 of relay 77 completes an energization circuit forwinding 83 of a relay 84, causing the contacts 85 of this latter relayto close. One terminal of each of the pigoperated switches 29 and 30(which are located adjacent the rack end of line 7; see FIG. 1) isconnected to a separate respective one of the two hot" inputs of a dualpulse shaping circuit 86 (which may be termed a bilogic controlcircuit"). The remaining terminals of these two switches are connectedtogether and in series with the relay contacts 85 to a common input 87of the circuit 86; thus, when contacts 85 are closed as above described,the pig switches 29 and 30 are rendered effective. Therefore, operationof the pig start pushbutton 64 results in pig-operated switches 29 and30 being set up or rendered effective. The dual pulse shaping circuit 86is a solid-state circuit, energized by means of connections (not shown)to the buses 35 and 37 and also to the a.c. power supply lines.

The primary function of the circuit 86 is to amplify and lengthen thepulses produced by momentary pig-actuated operation of the (normallyopen) switches 29 and 30, such that the enhanced pulses may be used toenergize or operate relays. Thus, when the pig, passing through line 7,closes and then opens switch 29, a pulse is developed on the circuit 86output lead 88 which flows through the winding 89 of a relay 90 andactuates this relay. Likewise, when the pig closes and then opens switch30, a pulse is developed on the circuit 86 output lead 91 which flowsthrough the winding 92 of relay 81 and actuates this relay.

Closure of contacts 93 of relay 77 completes an energization circuit forwinding 94 of a relay 95, causing the normally closed contacts 96 ofthis relay to open. One terminal of the pig-operated switch 22 (which islocated adjacent the source tank end of line 7, within pipe 16; seeFIG. 1) is connected to one of the two input leads of a pulse shapingcircuit 97 (which may be termed a monologic control circuit"). Theremaining terminal of switch 22 is connected in series with the relaycontacts 96 to the other input lead of circuit 97; thus, when contacts96 are opened as above described, the pig switch 22 is renderedineffective. Therefore, operation of the pig start" pushbutton 64results in pig-operated switch 22 being rendered ineffective. The pulseshaping circuit 97 is a solidstate circuit, energized via connections(not shown) to the buses 35 and 37 and also to the a.c. power supplylines.

Circuit 97 operates somewhat similarly to circuit 86, previouslydescribed. Assume for the moment that contacts 96 are closed, so thatthe description of this part of the circuit may be carried forward. Inthis case, when the pig closes and then opens switch 22, a pulse wouldbe developed on the circuit 97 output lead 98 which would flow throughthe winding 99 of a relay 100 and would actuate this relay.

Closure of contacts 101 of relay 77 completes an a.c. energizationcircuit for the solenoid winding 21 of the source tank end air supplyvalve 21, opening this valve. As a result, compressed air is admitted tothe'left-hand end of pipe 16, displacing the pig from its storedposition in this pipe and moving it through the loading line 7 towardthe rack end, pushing the product (oil) in this line into the truck 8.This tops off" the truck.

Relay contacts 63 being closed, operation of pushbutton 64 alsocompletes an energization circuit for a relay 102, from the positive bus35 through the lower pair of contacts 103 of pushbutton switch 64,through the winding of relay 102 to the negative bus 37. Relay 102, whenenergized, locks itself in through a pair of locking contacts 104 andthe normally closed contacts 105 of a time delay relay 106. The relay106 provides an on" time delay of 5 seconds, between the time itswinding is energized and the time its contacts such as 105 operate. Thenormally closed contacts 33 previously referred to, which are in serieswith the contacts of pushbutton switches 32 and 73, are operated byrelay 102. Thus, when relay 102 is energized as above described, thecontacts 33 open, preventing any circuit being completed by operation ofeither start" pushbutton 32 or stop pushbutton 73.

Energization of relay 102 also closes its contacts 107, completing anac. energization circuit through the pig on indicating light 108 on thecontrol panel 3. This light then goes on, indicating pig on, i.e., pigsystem in operation.

When the pig passes by the pig-operated switch 22 at the source tankend, this switch is closed and then opened as a result of such passage,but no action results because this switch is then rendered ineffectiveas a result of contacts 96 being open (relay 95 being energized at thistime).

When the pig, being pushed by the compressed air through line 7, passesby the normally open pig-operated switch 29 near the rack end of theline, this switch is closed and then opened as a result of such passage.Since contacts 85 are closed at this time (rendering switch 29effective), the opera- -tion of switch 29 actuates relay 90, opening itsnormally closed contacts 61. The opening of contacts 61 releases relay58,'opening its contacts 59 and deenergizing the solenoid 10' of ballvalve 10. The loading rack ball valve 10 then closes.

Actuation of relay 90 causes closing of its contacts 109, completing ana.c. energization circuit to the open coil 26" of rack vent valve 26.Rack vent valve 26 then opens to the slop sump, and latches open,simultaneously with the closing of ball valve 10 (previously described).

Relay 90, when energized, locks itself in through a pair of lockingcontacts 110, the normally closed contacts 111 of relay 81, and thenormally closed contacts 112 of relay 100.

When the pig reaches tee 9 it passes on into pipe 23. When the pigpasses by the normally open pig-operated switch 30, this switch isclosed and then opened as a result of such passage. Since switch 30 iseffective at this time (contacts 85 being closed), the operation ofswitch 30 actuates relay 81, opening its normally closed contacts 80.The opening of contacts 80 releases relay 77, opening its previouslyclosed contacts 101 and thus deenergizing the solenoid 21 of the sourceend air supply valve 21, causing this valve to close. This closes offthe compressed air which was pushing the pig, so the pig comes to a stopagainst the flange 24.

Actuation of relay 81 causes closing of its contacts 113, completing anac. energization circuit to the open" coil 19" of source vent valve 19.Source tank vent valve 19 then opens, and latches open.

Relay 81, when energized, locks itself in through a pair of lockingcontacts 114 and the normally closed contacts 112 of relay 100.

The opening of contacts 111 when relay 81 is energized releases relay90, which in turn opens its contacts 109 and removes the energizationvoltage from open" coil 26" of the rack vent valve 26.

As previously mentioned, the operation of pig-operated switch 30 by thepig results in the release of relay 77, opening its contacts 82 andreleasing relay 84; the contacts 85 of relay 84 then open and render thepig-operated switches (pig switches) 29 and 30 ineffective. Also, whenrelay 77 releases as aforementioned, its contacts 93 open to releaserelay 95, causing its normally closed contacts 96 to reclose. Thisrenders pig switch 22 effective. Thus, the pig switches or pigoperatedswitches are set up for a pig run from the rack end back to the sourcetank end; switches 29 and 30 are rendered ineffective and switch 22 isrendered effective.

The actuation of relay 81 (in response to closing of switch 30) alsocauses closing of its contacts 1 15, which completes an energizationcircuit for the winding 116 of a time delay relay 1 17, as follows:negative bus 37, winding 116, closed contacts 115, the normally closedcontacts 112 of relay 100, positive bus 35. After an on time delay of 1%minutes, relay 117 closes its contacts 118, and also closes its contacts1 19. It will be remembered that source vent valve 19 opens when relay81 is actuated. This time delay (of relay 117) allows the line 7 tobecome exhausted (via vent valve 19) before the pig is started backtoward the source tank end.

The closing of contacts 1 18, after the time delay, completes an ac.energization circuit for trip winding 26 of vent valve 26, causing thisrack vent valve to trip closed.

The closing of contacts 119 of the time delay relay 117 completes an ac.energization circuit for the solenoid winding 28' of the rack end airsupply valve 28, opening this valve. As a result, compressed air isadmitted to the right-hand end of pipe 23, displacing the pig from itstemporary position in this pipe, so that it starts its run back throughthe loading line from the rack end toward the source tank end.

When the pig passes by pig-operated switch 30 at the rack end, and alsopasses by pig-operated switch 29 at this same end, the pig operatesthese respective switches, but no action results in either case becausethese switches are at this time both rendered ineffective (contacts 85being open).

When the pig, being pushed by the compressed air from right to leftthrough line 7, reaches tee 6 it passes on into pipe 16. When the pigpasses by the pig-operated switch 22, this normally open switch isclosed and then opened as a result of such passage. Since switch 22 iseffective at this time (contacts 96 being closed), the operation ofswitch 22 actuates relay 100, opening its normally closed contacts 1 12.The opening of contacts 1 12 releases relay 81 and also deenergizesrelay 1 17, as well as releasing relay (if the latter has not alreadybeen released by actuation of relay 81).

The opening of contacts 1 19 when relay 117 is deenergized deenergizesthe solenoid 28' of the rack end air supply valve 28, causing this valveto close. This closes ofi the compressed air which was pushing the pigfrom right to left, so the pig comes to a stop in its home, pipe 16,against flange 17.

The opening of contacts 1 18 when relay 117 is deenergized removes thevoltage which was applied to trip" winding 26' of rack vent valve 26.

Relay 100, when energized, locks itself in through a pair of lockingcontacts 120 and the normally closed contacts 121 of time delay relay106.

Actuation of relay causes closing of its contacts 122, completing an ac.energization circuit to the open coil 26" of rack vent valve 26. Rackvent valve 26 then opens, and latches open.

Actuation of relay 100 also causes closing of its contacts 123, whichcompletes an obvious energization circuit for coil 124 of time delayrelay 106. After the S-second on time delay provided by relay 106, itscontacts open, and its contacts 121 open.

Opening of contacts 105 of relay 106 releases relay 102, which reclosesits contacts 33 to reset the pushbuttons 32 and 73 for the nextoperation. Opening of contacts 107 of relay 102 breaks the energizationcircuit through the pig on" light 108, causing this light to go out.

Opening of contacts 121 of relay 106 releases relay 100, which byopening its contacts 123 deenergizes cell 124 and resets relay 106 tothe position illustrated in the drawing.

The entire system is now reset for the next operation. The vents l9 and26 at the ends of the loading system are both open, all of the solenoidvalves are closed, and the pig is in its home" in pipe 16.

The pig-operated switches 22, 29, and 30 may be of the type known asUni-Tec Model lOO-S Detector, each including a hermetically sealednormally open proximity switch, a permanent magnet assembly, and ahemispherically shaped pressure balanced probe for bidirectionaloperation. A detector of this type is actuated when a pig in passingcauses the probe that projects into the ID. of the pipe to be displaced.This displacement of the probe from the ID. of the pipe raises thebalanced magnetic assembly into the vicinity of the proximity switch.The switch (housed in a calibrated tube), upon being influenced by themagnets, first closes, and then opens when the pig passes on by,lowering the magnetic assembly again. This operation of the switches 22,29, and 30 has been previously referred to in connection with thedescription of the circuit operation.

In the loading system of this invention, the pig used must negotiateseveral tee connections in the 4-inch line, such as at 6 and 9. It istherefore of a dual construction, such that it will span these teeconnections without losing air seal. Refer now to FIGS. 3 and 4, whichare a side view and an end view, respectively, of a pig which may beemployed in this invention. In FIG. 3, the pig is schematicallyillustrated at home, in pipe 16. The pig is based upon two identicalsolid round balls (spheres) 125 and 126 each 4 inches in diameter andpreferably made of the synthetic elastomeric material known as Neoprene.In this connection, it will be remembered that the pipeline 7, and thepipes 16 and 23, are all 4 inches in diameter.

A hole seven-sixteenths inch in diameter is drilled diametricallythrough each of the balls, in a direction perpendicular to the Neopreneball laminations, and in the assembled pig a &- inch diameter rod 127, 9inches long and threaded at each end, extends through the holes in thetwo balls. Thus, the balls are in effect mounted upon the rod 127 andare held together thereby, as will become apparent. The balls are spacedapart along rod 127 by means of a piece 128 of B-inch pipe whichsurrounds the rod, a pair of k-inch hardened round washers 129 beingutilized, one at each end of the pipe 128 and tack welded thereto. Byway of example, the subassembly of pipe 128 and washers 129 may have anoverall length (parallel to the axis ofrod 127) of2 inches.

A counterbore 130, l inch in diameter and about 1 inch deep, is formedat the outer end of the diametral hole in sphere 125, and in thiscounterbore a pennanent-type connection of sphere 125 to rod 127 iseffected. A w-inch hardened round washer 131 is placed over the end ofrod 127, and a regular hex nut 132 is threaded onto rod 127 and is thentackwelded to the threaded rod 127.

A counterbore 133, similar to counterbore 130, is formed at the outerend of the diametral hole in sphere 126. At this end, a lfi-inchhardened round washer 134 is used, followed by a lock washer 135 and ahex nut 136, which latter is threaded onto rod 127 and is thentack-welded to the threaded rod 127. It should be apparent that the twospheres 125, 126 are held together in spaced relation by means of theconstruction described, including items 127-136.

When the dual-sphere pig is traveling through a pipeline, only one ofthe spheres at a time will lose air sea] at a tee connection (the othersphere retaining seal at this time), so the net result is that the pigwill travel through tee connections without hanging up.

The invention claimed is:

1. A pig system comprising a fluid flow conduit of finite length, meansproviding a chamber communicating with one end of said conduit butoutside of the flow path of fluid being pumped through said conduit, apig normally resting in said chamber but adapted to sealingly movethrough said conduit, means rendered effective in response to manualoperation of a switch to cause said pig to move from said chamber intosaid conduit and through said conduit from said one end thereof, andmeans operating automatically, in response to the arrival of said pig atthe other end of said conduit, to cause said pig to move through saidconduit from said other end thereof to said one end thereof and backinto said chamber.

2. System according to claim 1, wherein said pig, when moving throughsaid conduit from said one end thereof, pushes liquid present in saidconduit toward said other end thereof.

3. System of claim 1, wherein the second-mentioned means comprises meansoperable to apply a pneumatic driving force to said pig.

4. System of claim 1, wherein the third-mentioned means includes meansoperable to apply a pneumatic driving force to said pig.

5. System of claim 1, wherein the third-mentioned means includes meansoperable to vent said chamber to atmosphere.

6. A pig system comprising a fluid flow conduit of finite length, meansproviding a chamber communicating with one end of said conduit butoutside of the flow path of fluid being pumped through said conduit, apig normally resting in said chamber but adapted to sealingly movethrough said conduit, a coupling between said chamber and a compressedair supply, said coupling including a first controllable valve; meansacting in response to manual operation of a switch to cause opening ofsaid valve, thereby to admit compressed air to said chamber to drivesaid pig from said chamber into said conduit and through said conduit, acoupling between the other end of said conduit and a compressed airsupply, said last-mentioned coupling including a second controllablevalve; means acting automatically, in response to the arrival of saidpig at the other end of said conduit, to cause opening of said secondvalve, thereby to admit compressed air to the other end of said conduitto drive said pig from said other end thereof to said one end thereofand back into said chamber.

7. System defined in claim 6, including also means acting automatically,in response to the arrival of said pig at said other end of saidconduit, for causing closing of said first valve.

8. System set forth in claim 6, including also a controllable vent valvefor venting said chamber to atmosphere, and means acting automatically,in response to the arrival of said pig at said other end of saidconduit, for causing opening of said vent valve.

9. System set forth in claim 6, including also a controllable vent valvefor venting said chamber to atmosphere, means acting automatically, inresponse to the arrival of said pig at said other end of said conduit,for causing opening of said vent valve, and means acting automatically,in response to the arrival of said pig at said other end of saidconduit, for causing closing of said first valve.

10. System of claim 6, wherein the automatic acting means includes aswitch mounted in said conduit and actuated by the passage of said pigthereby.

11. System defined in claim 6, including also means actingautomatically, in response to the return of said pig to said chamber,for causing closing of said second valve.

12. System of claim 11, wherein the means which acts automatically inresponse to the return of said pig to said chamber includes a switchmounted in said chamber and actuated by the passage of said pig thereby.

1. A pig system comprising a fluid flow conduit of finite length, meansproviding a chamber communicating with one end of said conduit butoutside of the flow path of fluid being pumped through said conduit, apig normally resting in said chamber but adapted to sealingly movethrough said conduit, means rendered effective in response to manualoperation of a switch to cause said pig to move from said chamber intosaid conduit and through said conduit from said one end thereof, andmeans operating automatically, in response to the arrival of said pig atthe other end of said conduit, to cause said pig to move through saidconduit from said other end thereof to said one end thereof and bacKinto said chamber.
 2. System according to claim 1, wherein said pig,when moving through said conduit from said one end thereof, pushesliquid present in said conduit toward said other end thereof.
 3. Systemof claim 1, wherein the second-mentioned means comprises means operableto apply a pneumatic driving force to said pig.
 4. System of claim 1,wherein the third-mentioned means includes means operable to apply apneumatic driving force to said pig.
 5. System of claim 1, wherein thethird-mentioned means includes means operable to vent said chamber toatmosphere.
 6. A pig system comprising a fluid flow conduit of finitelength, means providing a chamber communicating with one end of saidconduit but outside of the flow path of fluid being pumped through saidconduit, a pig normally resting in said chamber but adapted to sealinglymove through said conduit, a coupling between said chamber and acompressed air supply, said coupling including a first controllablevalve; means acting in response to manual operation of a switch to causeopening of said valve, thereby to admit compressed air to said chamberto drive said pig from said chamber into said conduit and through saidconduit, a coupling between the other end of said conduit and acompressed air supply, said last-mentioned coupling including a secondcontrollable valve; means acting automatically, in response to thearrival of said pig at the other end of said conduit, to cause openingof said second valve, thereby to admit compressed air to the other endof said conduit to drive said pig from said other end thereof to saidone end thereof and back into said chamber.
 7. System defined in claim6, including also means acting automatically, in response to the arrivalof said pig at said other end of said conduit, for causing closing ofsaid first valve.
 8. System set forth in claim 6, including also acontrollable vent valve for venting said chamber to atmosphere, andmeans acting automatically, in response to the arrival of said pig atsaid other end of said conduit, for causing opening of said vent valve.9. System set forth in claim 6, including also a controllable vent valvefor venting said chamber to atmosphere, means acting automatically, inresponse to the arrival of said pig at said other end of said conduit,for causing opening of said vent valve, and means acting automatically,in response to the arrival of said pig at said other end of saidconduit, for causing closing of said first valve.
 10. System of claim 6,wherein the automatic acting means includes a switch mounted in saidconduit and actuated by the passage of said pig thereby.
 11. Systemdefined in claim 6, including also means acting automatically, inresponse to the return of said pig to said chamber, for causing closingof said second valve.
 12. System of claim 11, wherein the means whichacts automatically in response to the return of said pig to said chamberincludes a switch mounted in said chamber and actuated by the passage ofsaid pig thereby.